During the drilling and completion of oil and gas wells, various wellbore treating fluids are used for a number of purposes. For example, high viscosity gels are used to create fractures in oil and gas bearing formations to increase production. High viscosity and high density gels are also used to maintain positive hydrostatic pressure in the well while limiting flow of well fluids into earth formations during installation of completion equipment. High viscosity fluids are used to flow sand into wells during gravel packing operations. The high viscosity fluids are normally produced by mixing dry powder and/or granular materials and agents with water at the well site as they are needed for the particular treatment. Systems for metering and mixing the various materials are normally portable, e.g. skid or truck mounted, since they are needed for only short periods of time at a well site.
The powder or granular treating material is normally transported to a well site in a commercial or common carrier tank truck. Once the tank truck and mixing system are at the well site, the dry powder material must be transferred or conveyed from the tank truck into a supply tank for metering into a mixer as needed. The dry powder materials are usually transferred from the tank truck pneumatically. In the pneumatic conveying process, the air used for conveying must be vented from the storage tank and typically carries an undesirable amount of dust with it.
Cyclone separators are typically used to separate the dust from the vented air. However, cyclone separators which are small enough to be included with a portable mixing system have a limited capacity for storing solids separated from the air. When the dust collection container is filled, the collected dust may fill or clog the cyclone separator and dust is undesirably vented with what should be clean air. To prevent undesirable dust discharge, the system must be stopped while the collection container is emptied.